The 1919 Schenck v. United States decision contains the most famous sentence ever penned by a Supreme Court justice—and one of the most dangerous. Affirming the conviction of socialists who urged draftees to resist fighting in World War I, Justice Oliver Wendell Holmes Jr. wrote: "The most stringent protection of free speech would not protect a man in falsely shouting fire in a theater and causing a panic." This was a flawed analogy—shouting "Fire!" in a theater incites action, whereas circulating ideas and arguments incites thought that might then lead to action—but one that has since been used as a justification for all manner of censorship.

Alex Kozinski, chief judge, Ninth Circuit Court of Appeals

The Court's interpretation of the Commerce Clause in Wickard v. Filburn—a 1942 case about a farmer who grew more wheat than the law allowed—led to a vast expansion of federal power, and was heavily relied on by those arguing last year that the Affordable Care Act was constitutional.

First National Bank of Boston v. Bellotti (1978) was the first case to officially grant corporations the First Amendment right to spend money in politics. Thirty-two years later, the majority ruling in Citizens United cited this case as precedent for the right of corporations to spend unlimited amounts on behalf of candidates, not just issues.

Scott Turow, attorney, author

Buckley v. Valeo (1976) struck down limits on campaign expenditures, which Congress had set in the wake of Watergate. The Court reasoned that campaign spending is not expressive conduct that can be regulated (like burning a draft card), but free speech protected by the First Amendment. Buckley created a permanent advantage for rich candidates, who could now spend all they wanted on their campaigns. Far more important, by treating expenditures as free speech, it set us on course to the justly lamented Citizens United decision of 2010.

The Supreme Court turns away thousands of cases every year, but letting these decisions stand means they could continue to generate bad precedent. In 1950's United States v. Munsingwear (a k a "the underwear case"), the Court articulated its power to strike lower-court decisions if they have become moot by the time they reach the justices' desks—a means of supervising and cleaning up our legal system.

Elizabeth Wurtzel, J.D., memoirist

The 1989 case Michael H. v. Gerald D. tells us what would happen if Justice Antonin Scalia wrote a Harlequin romance. We have a California model, her New York City husband, her boyfriend next door, her boyfriend down the road—and the daughter they all love. Scalia led the majority in siding with California law, which generally presumes a woman's husband to be the father of her children, regardless of anyone else's claims—because having a stable family matters more than biology.

Theodore B. Olson, former solicitor general

I'd go with a case the Supreme Court didn't take. In 1793, Secretary of State Thomas Jefferson asked the Court for an advisory opinion on whether the French minister could commission privateers in the U.S., despite President Washington's Proclamation of Neutrality. Chief Justice John Jay declined to issue one, on separation-of-powers grounds. This established the still-followed precedent for the judiciary to render decisions only on actual cases.

Kathleen M. Sullivan, former dean, Stanford Law School

Everyone has heard of Brown v. Board of Education, which held that segregation violates the Fourteenth Amendment. But that applies only to the states. It was Bolling v. Sharpe (1954), about segregation in D.C. schools, that found discrimination by the federal government to be a violation of the Bill of Rights. Any federal discrimination suit—for example, this year's case about the Defense of Marriage Act—descends from Bolling.

Andrew Cohen, Atlantic contributing editor

Decided in 1984, Strickland v. Washington created a procedural rule that makes it virtually impossible for a criminal defendant to successfully argue that he or she has been denied the "effective assistance" of counsel—and thus the Sixth Amendment right to a fair trial. The ruling is directly responsible for thousands of Americans' incarceration after trials in which their lawyers drank, or were using drugs, or were sleeping, or were otherwise clearly incompetent.

Diane P. Wood, judge, Seventh Circuit Court of Appeals

Americans who believe that their rights have been violated are entitled to turn to the courts for relief, aren't they? Not necessarily, according to the 1923 Supreme Court decision in Frothingham v. Mellon. This case launched the rule that requires taxpayers to show "particularized" injury, traceable to a legal violation that can be redressed. Frothingham has closed courthouse doors to people with complaints about government-supported religion, unconstitutional state tax subsidies, unlawful expenditures by the CIA, and a variety of environmental and other public-interest issues.

In 1819's Dartmouth College v. Woodward, Daniel Webster famously said in oral argument, "It is, Sir, as I have said, a small college. And yet there are those who love it!" Much less famously, the Supreme Court ruled that Dartmouth's establishment as a corporation was a contract with New Hampshire, so the state could not meddle with that charter and turn the private college into a public university. In writing that a "corporation is an artificial being" and "possesses only those properties which the charter of creation confers upon it," Chief Justice John Marshall anticipated a major controversy of our day—and indicated why the Roberts Court's treatment of corporations as equal to citizens is such a stretch.

Garrett Epps, novelist, legal scholar

Plessy v. Ferguson didn't say segregation must be "separate but equal"—only "reasonable." It was 1914's McCabe v. Atchison, Topeka & Santa Fe Railway Co. that brought "equal" into the mix. Black plaintiffs challenged a statute requiring separate railroad cars but permitting railroads to omit sleeper cars for blacks. Though the Court dodged the case on procedural grounds, it noted in passing, "If facilities are provided, substantial equality of treatment of persons traveling under like conditions cannot be refused." Without McCabe, the road to Brown v. Board of Education would have been harder.

Gerald Torres, professor, University of Texas School of Law

In 1879, John Elk renounced his allegiance to his American Indian tribe to go live among the citizens of Omaha. But when he tried to register to vote, the registrar claimed that he was not a citizen. No one disputed that Elk was born within the territorial limits of the United States, but in 1884's Elk v. Wilkins, the Court ruled that the citizenship clause of the Fourteenth Amendment did not apply to Elk or others like him. The Indian Citizenship Act of 1924 changed this, but the case remains relevant to today's birthright debate. Some suggest that the children of undocumented immigrants have no more claim to citizenship than Elk did. They are wrong.

This is an expanded version of May 2013's Big Question. Submit your own answer—or suggest a future question—by e-mailing bigquestion@theatlantic.com.